TBR: pipe2browser: Prepare all repos for open-sourcing.
TBR: pipe2browser: Prepare all repos for open-sourcing.

The CONTRIBUTING file is added to all repos, and also added
to the jiri-copyright tool so that repos can be automatically
checked and fixed.

I've run jiri copyright fix against all repos to fix up
outstanding issues.

MultiPart: 18/23

Change-Id: I6fb8edb9133c3f1975b53d4f8dcc66d4af24ab1a

vanadium/pipe2browser,vanadium/pipe2browser,vanadium/pipe2browser,vanadium/pipe2browser